1. Field of the Invention
The invention relates generally to the configurations and methods of manufacturing the semiconductor devices. More particularly, this invention relates to a gallium nitride (GaN)-based device implemented with new device configurations and manufacturing methods for providing reliable and high quality termination structure with guard rings formed by applying an epitaxial growth method.
2. Description of the Prior Art
The gallium nitride (GaN) based devices such as Schottky diodes have the advantage over silicon devices in achieving a high blocking voltage, while maintaining a low on-resistance using a small semiconductor die. However, conventional methods of configuring and manufacturing gallium nitride (GaN) based devices including Schottky diodes as a rectifying device, or devices for other functional applications are still challenged by a technical limitation of lacking controllable manufacturing processes to assure a reliable termination structure can be provided. At the edges and corners of a semiconductor die, there is a high electric field, so a termination structure is needed to ensure that breakdown occurs in the main portion of the device rather than at the edges, i.e., termination region. Due to the wide band-gap nature of the nitride semiconductor, reliable guard rings such as P-type guard rings cannot be conveniently provided by applying the conventional implant and diffusion processes commonly used with silicon based semiconductors.
In U.S. Pat. No. 7,229,866, entitled “Non-activated guard ring for semiconductor devices”, a semiconductor device with a guard ring is disclosed. FIG. 1 shows laterally conducting Schottky diode 100. The Schottky diode includes an electrically insulating substrate 102 and a buffer structure 104. A highly doped semiconductor layer 106 is disposed atop the buffer structure 104. A semiconductor contact layer 108, a lower doped semiconductor layer is disposed atop a portion of the more highly doped semiconductor layer 106. A Schottky metal contact 110 is located atop the semiconductor contact layer 108 and forms a metal-to-semiconductor rectifying junction with the semiconductor layer 108. A thicker bond pad metal layer 112 is disposed atop the Schottky metal contact 110. A guard ring 120 is formed within the semiconductor layer 108 and is located at or near the edge of the mesa. The guard ring 120 serves to reduce the high electric fields located at the edges of the Schottky metal contact as well as reduce the leakage current that occurs when the device is reverse biased. An ohmic metal contact 116 is disposed atop a portion of the higher doped layer 106, and a thicker bond pad metal layer 118 is disposed atop the ohmic metal contact 116. A passivation layer 114 may be formed at least between the stacked structure formed by the ohmic metal contact 116 and bond pad layer 118 and the stacked structure formed by the semiconductor layer 108, Schottky metal contact 110 and bond pad metal layer 112. The guard rings as shown are formed by ion implantation into the semiconductor contact layer without completely annealing the semiconductor contact layer to form a high resistance region. The guard ring may be located at the edge of the layer or, alternatively, at a distance away from the edge of the layer. A Schottky metal contact is formed atop the layer, and the edges of the Schottky contact are disposed atop the guard ring.
However, for the nitride semiconductor device, an edge termination structure implemented with guard rings 120 as shown in FIG. 1, when formed by ion implantations followed by thermal activation or even without thermal activation or diffusions, does not form a true P-type semiconductor region, but often become highly resistive or semi-insulative instead of the intended P-type semiconductor materials to carry out the guard ring functions. Furthermore, the highly resistive edge termination structures formed by the implant process are embedded with defects from the gallium nitride semiconductor, which causes poor reliability or poor unclamped inductive switching (UIS) capability.
There is an urgent demand to overcome such limitation especially for gallium nitride based Schottky diodes. As a rectifier, the Schottky diode is ideal for application to minimize the switching loss where the energy consumption occurs during the switch mode such as an application to a switch-mode power supply (SMPS) device. A SMPS device when implemented with GaN based Schottky diode can deliver greater efficiency of power utilization with reduced switching loss and with high blocking voltage. However, a reliable termination structure such as P-type guard rings formed close to the device edge near an anode electrode is necessary to assure high performance reliable operations. However, as discussed above, for those of ordinary skill in the art, reliable and high quality P-type guard rings are hard to realize for the GaN based devices. Conventional ion implantation and diffusion processes are not useful to form the guard rings with good quality and reliable performance.
For these reasons, there are demands to provide device configurations and manufacturing methods to provide high quality and reliable guard rings in the termination areas for the GaN based devices such that the above-discussed difficulties and limitations may be resolved.